Martin Nielsen, DVM, PhD, Dipl. ACVM, Schlaikjer professor of Equine Infectious Disease, associate professor in the University of Kentucky Department of Veterinary Science at the Gluck Equine Research Center, in collaboration with some of the leading parasitology researchers in New Zealand, recently published a study in the International Journal for Parasitology: Drugs and Drug Resistance.

In the study, he and AgResearch, New Zealand, scientists Christian Sauermann, Dave Leathwick and Mark Lieffering combined several computer simulations to study how climate change could affect horse parasites and drug resistance. During the study, the team combined their cyathostomin (small strongyle) simulation model with six different climate change prediction models.

Some of the key findings from the study:

• Shifting of seasonality will have a marked impact on parasite transmission patterns.
• This in turn can lead to larger parasite burdens in areas changing from temperate to warmer climates.
• The warmer climate and longer parasite transmission season can also affect development of dewormer resistance.
• Non-drug related strategies will become increasingly important for parasite control.

An excerpt from the study’s abstract:

Climate change is likely to influence livestock production by increasing the prevalence of diseases, including parasites. The traditional practice of controlling nematodes in livestock by the application of anthelmintics is, however, increasingly compromised by the development of resistance to these drugs in parasite populations.

This study used a previously developed simulation model of the entire equine cyathostomin lifecycle to investigate the effect a changing climate would have on the development of anthelmintic resistance. Climate data from six General Circulation Models based on four different Representative Concentration Pathways was available for three New Zealand locations. These projections were used to estimate the time resistance will take to develop in the middle (2040–49) and by the end (2090–99) of the century in relation to current (2006–15) conditions under two treatment scenarios of either two or six yearly whole-herd anthelmintic treatments.

The development of resistance varied between locations, time periods and anthelmintic treatment strategies. In general, the simulations indicated a more rapid development of resistance under future climates coinciding with an increase in the numbers of infective larvae on pasture and encysted parasitic stages. This was especially obvious when climate changes resulted in a longer period suitable for development of free-living parasite stages.

A longer period suitable for larval development resulted in an increase in the average size of the parasite population with a larger contribution from eggs passed by resistant worms surviving the anthelmintic treatments.

It is projected that climate change will decrease the ability to control livestock parasites by means of anthelmintic treatments and non-drug related strategies will become increasingly important for sustainable parasite control.

Their paper is available via open access here.